Length grading machines, or grain separators, are typically used to separate a stream of grain containing various types and sizes of grain into its constituent parts, for example, wheat, durum, oats, barley and rice, and/or to separate such grains from other seed contaminants. These machines employ a rotating member, or cylinder, having lifting pockets located along an interior surface thereof, for example, formed by indentations; the pockets, according to their size, receive and lift particular lengths, or sizes of granules out of a stream of grain having been fed into the cylinder as the cylinder rotates. A trough, called a liftings trough, is mounted within the cylinder, to receive the separated granules, which are lifted by the lifting pockets; the trough may include a conveyor, for example, a screw conveyor, to transport the separated granules out from the machine.
In existing length grading machines, lifting troughs have been made larger to handle an increased amount of lifted granules in order to increase separation process efficiency. However, such an enlarged liftings trough, rather than providing the desired increased efficiency, can, by restricting the flow of granules entering the rotating cylinder, cause inlet leakage and pinching that results in a reduced efficiency.